The invention relates further to an arrangement for cutting such a flat workpiece by means of a laser beam.
Conventional separation methods for flat glass are based on first generating a score in the glass utilizing a diamond or a cutting wheel in order to thereafter break the glass along the weakened location generated in this manner by an external mechanical force. It is disadvantageous with this method that particles (splinters) are separated from the surface by scoring which can then deposit on the glass and there, for example, lead to scratches. Likewise, so-called marrings can arise at the cut edge which lead to an uneven glass edge. Furthermore, the microtears in the cut edge, which arise when scoring, lead to a reduced mechanical durability, that is, to an increased danger of breakage.
An approach for avoiding splinters as well as surface fractures and microfissures comprises separating glass on the basis of thermally generated mechanical stress. Here, a heat source is directed onto the glass and is moved relative to the glass at a fixed speed and thereby builds up a thermomechanical stress to such a high extent that the glass forms fissures. The necessary characteristic of the heat source to be able to position the thermal energy locally, that is, with an accuracy of better than a millimeter (which corresponds to the typical cut accuracies) is satisfied by infrared radiators, especially gas burners and especially lasers. Lasers have been proved and are in use because of their excellent focusability, good controllability of the power as well as the possibility of the beam formation and therewith the intensity distribution on the glass.
This laser cutting method induces a thermomechanical stress up to beyond the resistance to breakage of the material via a local warming with the focused laser beam in combination with a cooling from the outside. This laser cutting method is known from several publications. For example, reference is made to DE 43 05 107 C2.
This method distinguishes basically from the laser cutting methods known, for example, from EP 0 062 482 A1 or U.S. Pat. No. 5,120,926 wherein a melting of the glass takes place while forming a cutting groove. The cutting groove is continuously blown clean by a gas.
The first-mentioned laser beam cutting method has proved itself as the superior method for different reasons and has prevailed in practice. It is from this method that the invention proceeds.
Typically, a so-called start score or initial score is needed at the start of the desired cutting line in that, typically, a weakened location is generated mechanically on the glass surface or at the glass edge with a scoring tool, that is, a score is formed. The thermomechanical stress, which is built up by the laser beam on the cutting line leads then to a break of the glass which proceeds from the weak location. The generation of this initial score is, for example, described in U.S. Pat. No. 4,044,936.
In the known case, the initial score is generated with an interrupted relative movement between the laser beam and the flat workpiece to be cut, that is, a “momentary standstill” in a scoring process which is completely separate in that the scoring tool is pressed with a pregiven mechanical force onto the glass surface.
The disadvantages of the known method are:
The duration of the cutting method is extended in each case by some seconds because an initial score must be generated in advance of each laser cut. Furthermore, the duration of forming the score is relatively long so that the problem of damage of the glass with the formation of splinters arises.